1. Field of the Invention
The field of the invention is that of guidance devices placed on board autonomous vehicles or robots, notably of the type that have to move about in environments that are inaccessible or dangerous to human beings.
If the environment in which the robot is moving is encumbered with obstacles, then the robot has to be provided with equipment for the acquisition, in real time or almost in real time, of information relating to this environment. This information may be either 2D or 3D information and enables the robot to explore and recognize its environment, move about in avoiding obstacles and plan its path.
2. Description of the Prior Art
There are known optical (video) type or acoustic type sensors fitted to autonomous robots. These sensors enable the acquisition of data relating to the environment in which the robots are moving.
Such sensors may consist, for example, of telemetrical lasers, acoustic or infra-red proximity or anti-collision systems, TRIDENT (protected name) type positioning systems using beacons, GPS (protected name) type positioning systems using satellites.
Video and acoustic sensors have the advantage of being low-cost devices that take up very little space, have excellent angular resolution and transmit data to the robot at a high bit rate. Good angular resolution makes it possible for a processing system associated with the video or acoustic sensors to locate distant objects as well as near but small objects.
However, video sensors and acoustic sensors both have limitations that bar their use on mobile ground robots.
Thus the performance characteristics of video sensors have the drawback wherein the measurements made are dependent on weather and environmental conditions. In particular, the qualities of the video sensors deteriorate in the presence of dust clouds or, again, the reliability of the data sent differs notably, depending on whether these video sensors are used by day or by night (i.e. through infra-red video sensors).
Furthermore whereas, in clear weather, the data transmitted by the optical sensors undergoes identical atmospheric attenuation (of the order of 0.2 dB/km) by day or by night (with infra-red sensing), in foggy weather this atmospheric variation is very different depending on the type of optical sensor used:
______________________________________ daytime sensor: attenuation = 150 dB/km nighttime sensor: attenuation = 100 dB/km ______________________________________
Optical sensors thus have the drawback wherein they are incapable of being used outdoors in all weather since their characteristics are excessively dependent on atmospheric conditions and on the environment in which they are used.
Another drawback of video sensors is that they do not display conformity with maps of the ground. Thus, such sensors cannot be used to explore an already explored zone.
The major drawback of passive and active acoustic sensors, for their part, is that they have very limited possibilities of analysis in distance, so much so that they cannot be used to locate objects or obstacles at a great distance.
Finally, both video sensors and acoustic sensors as such are incapable of carrying out environmental recognition operations, for example in relation to an onboard map. To do so, they have to be associated with shape recognition algorithms. Now, this type of function calls for substantial and bulky computing means which are hardly compatible with the compactness and mobility required in onboard applications.